Helicopter automatic flight control



April 24, 1956 B. KELLEY 2,743,071

HELICOPTER AUTOMATIC FLIGHT CONTROL Filed Dec. 2, 1952 2 Sheets-Sheet l SER1/0 46 (Opf/ana@ I ,Lgf- 2 EAW/ QAM A/ELLfV BY ,47' 7' ORNE KSZ April 24, 1956 B. KELLEY HELICOPTER AUTOMATIC FLIGHT CONTROL 2 Sheets-Sheet 2 Filed Dec. 2, 1952 IN VEN TOR.

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United States Patent O HELICOPTER AUTOMATIC FLIGHT coNTRoL Bartram Kelley, Dallas, Tex., assignor to Bell Aircraft Corporation, Wheatiield, N. Y.

Application December 2, 1952, Serial No. 323,644

Claims. (Cl. 244-17.13)

This invention relates to rotary wing aircraft, and more particularly to means for converting a helicopter aircraft which is inherently non-stable in ight into a stable type.

Experience has shown that most helicopter aircraft, when in forward Hight with the pilot stick either locked or held inattentively by the pilot, tend to oscillate phugoidally in a manner commonly referred to as porpoising. If such oscillations are not countered by skillful application of controls by the pilot, they increase automatically in amplitude and violence, divergently from the intended flight path, and soon result in a dangerously unstable flight condition. It is the primary object of the present invention to provide in a helicopter aircraft or the like, means operating automatically tov damp the aforementioned oscillations so as to cause the aircraft to tend to return to a straight line flight path subsequent to any disturbance therefrom without attention by, the pilot, thereby giving the aircraft inherently stable Hight characteristics. Other objects and advantages of the invention will appear from the specification hereinafter.

In the drawing:

Fig. 1 is a fragmentary schematic illustration of one exemplication of the present invention in a single rotor type helicopter aircraft;

Fig. 2 is a fragmentary section, on an enlarged scale, taken along line II-II of Fig. 1;

Fig. 3 ,is a graphical illustration of three diiferenttypes of helicopter ight paths, which will be referred' to hereinafter for the purpose of explaining the need for and the effect of the present invention; and

Fig. 4 is a fragmentary schematic elevational view of a rotor control arrangement of the present invention as applied to a tandem rotor type helicopter aircraft.

The invention contemplates, broadly, provision of a vertical acceleration-responsive inertia device in the aircraft connected into the rotor blade cyclic pitch control system in such manner as to react to vertical' accelerations .thereon by introducing pitch ,corrective control motions into the rotor blade cyclic pitchk control system prior to full development of the phugoid oscillation producing effects which are set up by the disturbance.

"Thus, whereas it is contemplated that the automatic control arrangement ofthe present invention is applicable with equaly facility to yall current typehelicopter or other rotary typeaircraft and the like, for purposes of illustration` herein the invention is shown for example in Fig. 1 as being -employed in conjunction with a single rotor type helicopter having a rotorrmast or drive shaft as indicated at 10 which mounts a rotor hub as indicated at 12 which in turn carries a pair of diametrically opposed rotori blades extending radially therefrom as indicated at 14` (Fig. 2). The rotor hub 12 is mounted upon the drive.

shaft or mast' 10 for'universal inclination thereon by means of any suitable device such as a gimbalring 13 as shown in U. S. Patent 2,368,698, or the like; while being at the same time pinned to the shaft 10 so as to rotate therewith in response to power applied to the drive ICC shaft through means of the aircraft engine (not shown).

The rotor blades 14--14 are connected to the hub 12 by means of bearing devices 15 permitting the blades to be rotatable relative to the hub 12 about the long axes of the blades for rblade pitch change purposes. A pitch control horn 16 extends from each of the blades into pivotal connection with a link device as indicated at 18, which in turn connects in each case to one end of a corresponding rockerrarm 20. The rocker arms 20-20 are pivotally mounted as indicated at 21 upon the upper end of a sleeve 22 which has a vertical spline connection with the mast 10 and therefore rotates therewith while being vertically slidable thereon. As shown, the opposite end of each of the rocker arms 20 is pivotally connected as indicated at 26, for cyclic pitch control of the blades and hence longitudinal and lateral control of the aircraft, to a link 27 extending from the outer race portion of a swash plate device28 which includes bearings 29 and an inner race 30.

The inner race 30 is in the form of a ring which is centrally bored to parti-spherical form so as to complement a parti-spherically shaped bearing portion 32 carried by the upper end of a sleeve portion 34 extending from rigid connection with the xed aircraft structure and encircling the drive shaft and sleeve unit lil-22. A push-pull member as indicated at 36 connects to the inner race 30 of the swash plate device and extends downwardly into the aircraft body and then into pivotal connection as indicated at 37 to one end of a bell crank 38 which is fulcrumed upon the fixed aircraft structure and which pivotally connects at its other end to a push-pull member 40. Whereas, the swash plate type device has been shown and described as being mounted on the mast 10 by means of a ball and socket type bearing, it will be understood that any other suitable mounting device may be employed, such as for example, a Cardan joint device or the like.

Whereas, the other end of the push-pull member 40 might be connected to the pilot control stick as indicatedy at 42 for longitudinal pitchy control of the aircraft with the inertia device of the invention connected thereto in any suitable manner, in the case of the present illustration the member 40 pivotally connects as indicated at 44 to a differential mechanism including a mixing lever 45 p which is in turn pivotally mounted as indicated at 46 upon a crank arm 48. The crank arm 48 is inturn fulcrumed upon the fixed aircraft structure as indicated at 49 while the other end of the mixing lever 45 is pivotally connected as indicated at S0 to a push-pull member 52, the other end of which pivotally connects as indicated at 53 to the pilot control lever 42 which may be fulcrumed upon the fixed aircraft structure as indicated at 56. -v

The crank arm 4S includes a horizontal arm portion 58 upon which is hung a weight 60 at a position which is both ahead of the overall center of gravity of the aircraft yand out of vertical alignment with the pivotal mounting 49 of the crank arm 48 on theaircraft frame.` Thus, as shown in the drawing the weight 60 tends to bias the crank arm to rotate in counterclockwise directionv as viewed in Fig. l about the pivotal connection 49; but a counterbalancing spring device as indicated at 62 is also provided in connectionrto the crank arm 48 to normally hold the crank and weight unit as in the position shown.

A tension adjustment cable 64 is preferably arranged to run from the spring, as around pulleys 65-66, and then into an adjustment screw device as indicated at 68 so that` may of course be also provided to be responsive to lateral movements of" the pil'ot control' stick 42 and' so coupled to the swash plate unit 28 as; to tilt it laterally for corresponding lateral maneuvering C Qntrol. (Ji-.thei aircraft, aS

is also. well kuownin. the art. .As indicated at 70.; a

Servo. device may be. included in coniuncticnwith the pushfpull. member.. 40, it; desired,` toboost thev forces. of the pilot controlledsystem.V

It. willA be.` notedthat the diterential. mechanism mterconnects. the weight. 6 0. and. the pilotY control. Stitk- 42tofthe. algebraic Sumpf. the respectivementmagnitudes.

Thuslitwill be. appreciated thatwithiheweight 60 and the spring 62.so, selected and-.relatively adjusted as to normally balancethe control linkage: system in; an attitude such asisillustrated;inl-iig. l,` any pilotactuations of the.

pilot` control stick. 42. will. thereupon. cause the mixing lever 45 to be oscillated upon its pivot; connection 46. Such movement of the control yarm will bcrin turntransmitted through the memberl 40, and the crank 38. to the push rod 36 thereby causing the, Swash plateunit 2,8ttoL be correspondinglyl tilted on its. bearing 3,2 relative to the fixed structure of theaircraft. In turn, such tilting of the swash plate will cause the appropriate rocker arm'ZO to be rocked upon its pivotal mounting on the sleeve 22, whereby the corresponding pushfrod 18. will. actuate the. corresponding rotor blade pitch control horn for` causing the rotor blades to rotate. in their pitch change bearings cyclically as the rotor revolves about the vertical center line of the-drive shaft 10., The rotor will be thereby controlled to provideV varying effective angles, of. incidence, of the respective blades asthey revolve cyclically about the rotor mast.

Thus, it will be appreciated that,inclusionof` the mechanism of the present invention in conjunction with. the. conventional controlv system. will not interfere with pilot operation ofthe latter for-aircraft maneuveringpurposes; while at all times, without attention by the pilot, the weight 60 is automatically attentive, to any, vertical accelerations. of the aircraft and4 will operate automatically to adjustthe rotor blade cyclic pitch control system to` counter the acceleration movements of the aircraft. For. example, assuming that the, aircraft is flying forwardly in a substantially horizontal flight path, and that it is sud-A denly disturbed by a gust or the like end pitches upwardly, the weight 60 willlag behind. the vertical jump" ofthe aircraft due to theinertia. of the weight. Thislagging behind of the weightwilt automatically cause thev lever 48 to rotate in counterclockwise,direction aboutgthepivot 49 thereby transmitting throughthe rod 40, a control mo.-` tion tending to tilt4 the swashplate, 38, ,due to thefact that.

the pilot control sticktends toremain` fixed in its previous attitude relative to the aircraft frame. For thispurposethe pilot control stick is preferably provided with Ia; small amount of friction and/or adjustable centeringl springsY (not shown) as is. well known in theart. The control system is so designed and constructed that such. a, control motion imparted to the svvash plate` control systemwill tilt the latter in such manner as` tocause therotor blade cyclic pitch change devicesto operateto Cause therotor to pitch downwardly, thereby offsetting. or countering the rising motion of the, aircraft. Similarly,.' 1ny 'disturbancesv causing downward pitching; ofthe aircraftfwill be; automatically accompanied by upwardor clockwise pivoting.

ofthe crank arm 4.8', resulting. in. ccr'resncndingadiustments ofthe blade pitch control swash plate so. as to counter the, oscillatingtendencies, so induced...

It will bc appreciated that the. spring` 625 andthe .weight 601.0fEig. l. will be. preselected seas tcbeof sucluclnar.-` actcristies. as` to, give. relatively. Senstiveireactionto. any.

vertical. acceleration.tendencies.. Rrcferablv,. the: action1 P ofthe` aceelerationfresponsive. weight. :nass`` 60 will hev damped, as for example by means of a suitable friction damping device as indicatedatl 72- through connection as indicated at 73 with crank arm 48. For collective con trol of the pitch of the blades of the rotor a control arm as indicated at 74 is coupled to the sleeve 22 through a suitably slotted portion of the collar 34.

lt is of course essential that this acceleration countering control effect be so timed as to act in the manner of a damping influence against the phugoid oscillating influence which is normally set up by the disturbing, gust or the like as distinguishedfrom being cumulative thereto.

Fig. 3 illustrates graphically the effect of the present invention. Inthis illustration, they curve designated 75 illustrates the deviations from a flight pathwhich a conventional helicopter aircraft or the like may take in respense to a Hight path disturbing gust, if the aircraft is of neutral stability characteristics. Thus, as shown in Fig. 3 whenever the aircraft is disturbcdby. an oncoming, gust or the like as aty point Aon curve, 7.5, the rOtOI islhfreby tilted upwardly and is, accompanied by. the. fuselage. in.

assuming an upwardly pitched attitude.. The. ightph thencurves upwardly. and crestsasndCated atB and then. starts to decline as indicated at` @and thereupon con:

tinues to oscillatewith substantially constant veloCitM and.. amplitudesv aboveV and. below. the horizon of the original. straight line flight path, On the other hand, asillUStratQCl by curve 76, whenever a helicopter aircraft. embodying the present invention is metby an oncoming gust and pitchesy upwardly, the accelerationsresponsive control device 0f the present invention then goes into, operation automatically such as `at the position .indicate/dat DV on thecurve 76 whereby to anticipate` and repuls. the forces` normally.

producing phugoidal oscillation of theflight path.

The essential feature of` the operation, of the device` lies lin the timing of its action, whichis suchas. to. anticipate. the motions of thel helicopter. For example, if theweigllt 60 were to be located at the center 0f gravity of the ma:-

chine, maximum effect would be produced at or slightly past the point B of curve 75. If the weight` 60.. is located forwardly of the aircraft center Qfgravity, thenthe fuselage pitching accelerations will` also affect it,V causing` its.

maximum effect to occur slightly before. point B., Such as. at D of curve 75. This phase relationship is essential.to proper operation of the device. Thus, the control mecha: nism of the present invention suppresses the tendency of the aircraft to oscillate, in itsflight path as shown. by Curve,

75, and operates to damp the tendencies to. Oscillation both above and below the plane of the original horizontalt dicated for example by curver 77 ofFig, 3. Thiscurve illustrates how. the oscillations of inherently unSLahlQhlicopter aircraft tend to constantly increase invelocity and amplitude, and therefore require, strict and expert counter control by the aircraftl pilotinorder to. avoid disasterin the absence of a device of the present invention., Itistto. be understood that, Whilethe. embodiment ,illustrated by the..

drawing herein involves. location of, the: acceleratiQn der.

Vvice forward ofjthe centeroi gravity of the aircrafhthns; causing maximum, response. before. the: aircraftl reaches` peint Br Fig.. 3; itis. possible that .the device; could.. beadf vantageously locatedat or even aftof the .center ofgravity,` depending on. the. naturalflight characteristics. of the, air-.

craft involved..

Fig. 4 illu8rates, application `of' the invention tofa tam dem rotor tvpehelicepter. aircraft wherein the rotor sysw tem of the aircraft is,.illustra tedto comprise-fref-and aft` dicated generally" affitta-861m. the mauncrfof: thelrutor arrangement of Fig,4 l. The-bladestoff; the'rotora-arcf-pitch.

adjustable by means of push-pull rods 87--88 connected to levers 90-92 which are fulcrumed upon vertically shiftable sleeves 94-96 and controllable by links 9798. The links 97`98 extend from the outer races 99-100 of swash plate devices 102-104 which are mounted for universal inclination relative to the masts, as by means of spherical ybearing devices 106-108 carried by sleeves 1094-110 encircling the corresponding rotor drive shafts 80-82.

The swash plates 102-104 are in turn controlled as to theirinclinations relative to the masts 80--782 by means of push-pull rods 112-114 which connect through means of bell cranksll-lltl to a common pushpull rod 120. The rod pivotally connects as indicated at `122 to the central portion of a mixing lever 124 which is fulcrumed as indicated at 126 upon a crank arm 128 which is in turn fulcrumed uponk the fixedv aircraft structure as indicated at 129. The free end of the mixing lever 124 is pivotally connected to a push-pull member 130 which in turn pivotally connects as indicated at 131, for longitudinal pitch control ofthe craft, to a cyclic pitch control pilot lever 132 which is fulcrumed to the aircraft structure as indicated at 133. The crank 128 is provided with a laterally extending arm portion 134 which carries thereon a weight mass as indicated at 135; and a tension spring 1381i's1connectedto the arm portion 134 and to the fixed aircraft structure so as to counter-balance the weight of the mass 135 so as to normally' maintain the crank arm 128 in the attitude substantially as shownin Fig. 4. A-

damper as indicated at 139 is preferably coupled to the crank arm 128 to damp the movement thereof as explained in connection with the damper installation 72 of Fig. 1.

In this tandem rotor arrangement provision for control ofthe rotor blade pitch system collectively is illustrated as comprising a pilot control lever 140 which is fulcrumed upon the fixed aircraft structure as indicated at 14.1 and connected to a push-pull member 142 which interconnects a pair of bell cranks 144 which in turn actuate push-pull members 146-148 leading into pivotal connections .as indicated at 149-150 with levers 151-152. These levers are fulcrumed as indicated at 153--154 upon links 155-156 which in turn connect respectively to bell cranks 1577--158 arranged to be actuated by a push-pull member 160 which in turn is actuated by a lever 162 fulcrumed upon the aircraft frame intermediately of its ends and pivotally connected as indicated at 164 to the pushpull. member 120 previously referred to. v However, it is to be noted that the bell crank and pushpullv members 157, 158, 160 are interconnected so as to provide av dillerential type operation of the bell cranks 157e-158 responsive to movement of the push-pull member V160, whereby the bell crank members are driven to pivot simultaneously but in opposite directions by movef ment of the push-pull member 160. Thus, for example, movement of the pushpull member 160 from left to right as shown in Fig. 4, will cause the bell crank 157 to rotate in counterclockwise direction while the bell crank 158 is simultaneously caused to rotate in` clockwise direction. Reversely, movement of push-pull member 160 from right toleft as viewed in Fig. 4 will cause the bell crank 157 to rotate in clockwise direction While the bell crank 158 is caused .to rotate in counterclockwise direction.

The free end of the rocking lever 151 is pivotally connected asA indicated at 166 to a push-pull member 168 whichpivotally connects as indicated at 169` to a pin device extending integrally from the vertically reciprocable sleeve 94; the pin connection device 169 being extended through a vertically slotted portion of the outer sleeve i structure 109. Similarly, the rocker beam 152 is pivotally connected as indicated at 172 to a push-pull member 174 which in turn pivotally connects as indicated at 176 to a pin device extending integrally from the inner vertically reciprocable sleeve 96 through means of a vertically slottedr portion of the outer sleeve 110.

Thus, it will be appreciated that when the collective pitch control lever 140 is pulled up and rearwardly, for` cranks 144-144 to rotate in clockwise direction with consequent raising of the collective pitch control sleeve 94-96 by virtue of the linkage connections thereto referred to hereinabove; the pivot points 153-154 functioning thereupon as fulcrum points for the levers 151-152. Hence, pilot-operation of the lever 140 will procure simultaneous pitch change adjustments of the effective angles of incidence of the rotor blades of both rotor units for hovering and vertical ascent-descent control of the aircraft; the collective pitch adjustments of the rotor blades of the respective rotor units being, under such circumstances, substantially equal in degree and in the same direction.

However, due to the linkage system comprising the beam 162 which pivotally connects to the push-pull member 120 and then to the bell cranks 157, 153 and then into thek differential collective pitch control mechanism whenever a cyclic pitch control effect is established as for example by pilot-manipulation of the control lever 132, the collective rotor blade pitch control devices of the respective rotor units are simultaneously affected differentially. The arrangement is such that whenever the pilot presses forwardly on the control lever 132 for cyclic control of the rotor units in order to obtain a forward traveling component in the lift force system, the rotor blade collective pitch control system is thereby simultaneously adjusted in such manner as to slightly decrease the pitch adjustments of all of the blades of the forward rotor unit while simultaneously increasing the pitch. adjustments of all of the blades of the aft rotor unit. This immediately establishes a forward andv downward pitching couple force acting on the aircraft tending to lower the nose and to raise the tail of the aircraft.

Then, upon pilot-adjustment of the cyclic control stick 132 rearwardly, as for the purpose of terminating the forward flight progress, the blades of the rotor units are ythereby cyclically adjusted as to pitch so as to bring both rotors back to horizontal attitudes for simple hovering flight of the aircraft. Simultaneously therewith the differential control mechanism' will operate to adjust the collective pitch control devices of the rotor units so as to equalize the collective pitch adjustments of the blades of the respective rotor units, so that the craft returns to a level attitude for hovering flight.

Similarly, any automatic adjustments of the rotor control mechanism such as may be introduced during flight by virtue of operation of the device of the present invention, as in response to acceleration-induced motions of O the mass weight 135 relative to the airframe, will be introduced into both the cyclic and collective pitch change control mechanism described hereinabove for simul taneous coordinated adjustments of the cyclic and collective pitch control mechanisms of the fore and aft rotor units.

In lieu of the combination cyclic and collective pitch control system hereinabove described in connection with tandem rotor type helicopters it is contemplated that the acceleration-responsive device of the invention may be' employed in a tandem rotor'type helicopter in control of only the collective pitch control of either one of the rotors. For example, the device may be connected solely to the collective pitch controlsystem of the forward rotor; and in such case whenever the aircraft pitches upwardly the acceleration-responsive device operates automatically to reduce the pitch of the blades of the front rotor, thus counteracting the pitching motion. Or, it may be connected to the collectivel pitch control system of the rear rotor to increase the pitch of the rear rotorl when the ship pitches upwardly to counterv the porpoising tendency of the craft.

Whereas, the invention has been illustrated and described only in conjunction with a Young type rotormechanism. as..- disclosed for example in-YU. Patent` 368;698; it. isI to bef understood. that the; invention is applicable with` equal facility to any other type helicopter: rotor or rotary wing system. Forexarnple, the invention is equally. applicable to helicopter.I aircraft wherein the,

rotor, hub, is rigidly attached to: therrotor mast or driveV hereinabove, for` cyclic as well asV collective pitch control and coupled toboth the conventional pilot controls and tothe. vertical. motion acceleration-responsive mechanism4 of-.thepresent inventionlas: explained hereinabove, Thus, any tendencies of the aircraft to pitch away from the intended; flight path will. be automatically and instantaneously. anticipated and countered by automatic operation.

of. the,- acceleration responsive control mechanism of the invention.

It; will be appreciated; that the. weight mass.l as` illus:- trated atti() (Fig. l) andA at 135 (Fig. 4) may take any convenient form, andmay comprise an otherwise usefull weight as for example the aircraft. storage battery. or, the

like )if preferred. Also, it will be appreciated that the.

weight. mass may be connected to the` cyclic and differential'collective. pitch control systems in any other desired.

manner, such as` for example by xing it directlyupon the pilotcontrol lever provided of course itis out of. vertical alignment with the mounting lever. pivot, so as toA be responsivey to vertical. accelerations` of the aircraft. It is also, to. he understood that whereas in Fig. lof the drawing, the accelerationrresponsive. weight device is shownas being connected only into the cyclic control sys-` tem; it may in like manner be connected only into the collective control system leading to the member 74 of Fig. l, or in combination therewith and with the cyclic control system.

'Hence, itwill be understood that although only afew forms of the, invention have been illustrated and described hereinabove it will be apparent tothose skilled in the art that the. invention is not so limited but that various changes may be, madeY therein without departing. fromme spirit of the. inventionor the scope of the appendedclairns.

.What is claimed is:

l. Ina helicopter aircraft or. the. like, the combination mechanism for adjustment thereof, pilotfoperable. conr trol means, inertiameans mountedon said aircraft for movement relative thereto in response to acceleration of said aircraft in cither'vcrtical direction, and .means including a differential mechanism operatively connecting` both saidpilot-operablc control means and said inertia means to said pitch control system for actuation thereof, said differential mechanism having a pair of independently operable input control elements and an output Control element in which-the output magnitude is a function of the algebraic sum oftherespectivc input magnitudes, said pilot-operable control means being connected tolopcrate one of said input control. elements, said inertia. means being connectedto operate the, other of said input control elements, and said. output. control elementbeing con nccted to operate saidpitch controlsystem.

2. The. combinationset.forthin claim l, together with damping. means operatively connected to. said. inertia means to damp theaction thereof.

3. The combination set forth in claim l, wherein said inertia` means ispositioned ahead of the center of gravity of the. aircraft.

4. in a helicopter aircraft-or the like, the combination comprising a bladed lift rotor mounted upon the. aircraft, aicycliepitchchange mechanism for, said rotor, acyclic pitch control i system operatively` connected `to said cyclic pitch. change, mechanism for adjustment thereon. Pilot--A operable control means, inertia. means mounted ou Said. aircraft' forsmovernent relative thereto in response toren celerationof said-aircraftvin either vertical directiomtandl meansincludiug, a differential mechanism operatively con.-. necting bothvsaid pilot-operable control meansand said.`

inertia moans-.toasaid cyclic. pitchcontrol systemffor actu-'- ationfthereof, said dilerential mechanism havingl a pain of independently operable input control elements andan output control element` in whichthe. output magnitude' is a function ofthe algebraic, sum of the. respective.. input; magnitudes, said pilot-operable controlmeans being: Con'- nected to operate one of said input control elements, said. inertia means being connected to. operate the. other ofsaid input, controlvelements,Y and said` output control. elemont beinggconnefcted` to operate. said pitch control system.

5. In` a helicopteraircraftY onthe'like, the combination; comprising abladed lift. rotor mounted .upon the. aircraft, a collective pitch change, mechanism for said. rotor, a. collective pitch control system operatively connected to.

said. pitch change mechanism for adjustment, thereof,`

pilot-.operable control means,Y inertia means mounted 0n. said, aircraft for movement relative thereto inresponse. toracceleration'oi'said aircraft in either vertical. direction,4 and means. including a differentiali mechanism operativeiy connecting; both said: pilot-operable4 control means and said inertia means to. said collectivepitchtcontrol,system, for actuation thereof, said differential mechanismt having a. p airof independently operable input control` Velementsand. an outputcontrolelcment in which the.ont.

put magnitude. is` afunction of the algebraic,4 surnofjthe respective; input magnitudes, said pilot-operablecontrol. means being connected to. operate one ofsaid. inputoontrol elements,4 said inertia means being` connected to. op.- eratethe other of said input control elements,v and said. output control element being connected tov operate. said4 pitch control system.

6. In a helicopter aircraft or thev like, the combination comprising aplurality of bladed lift rotors mounted upon. the aircraft, pitch change mechanisms for saidrotors,..a pitch control system operatively connected, to saidlpitcli change. mechanisms for adiustments thereof, pilot-oper-4 able control rneansinertia means mounted on.said airf craft for movement relative thereto ini response toraccelerationY of said aircraft in either vertical direction.. andA means including a differential mechanism` operatively connecting both said. pilot-operable control means` and said inertia means to said pitch control system for like actuation of said pitch mechanisms, saidA differential mechanism having a pair of independently operable input control' elements and an output control element in which the. output magnitude is aV function. of the algebraiosuin ofthe respective input magnitudes, said pilot-operable' control means being connected to operate one. ofsaid input control elements, said inertia means being connected to operate the other ofsaid input control`elemcntsand` said output control element being connected to operate said pitch control system.

7. In a helicopter aircraft or the. like, the combination comprising a plurality of bladed lift rotors mounted upon. the. aircraft, a pitch change mechanism for. each of said rotors, a pitch control system. operatively connected to saidpitch change mechanisms, for adjustments thereof; pilot-operable control means, inertia: means mounted-on said aircraft for movement relativer thereto in response to acceleration of saidaircraftineither'ver-l tical direction, and" means including a ditferentiallmech'a'- nism operatively connecting bothV said pilot-operable control means and said'inertia' means .to said pitch control" system for different actuation of said pitch .change mecliani'sms, said differential mechanism having a pair of.`i` n dependently operable input control elements and an, out'-, put control. element in which the output magnitude is` a function of the algebraic sumnof the respective, input magnitudes, .said pilotoperable. control means beingconnected to operate one of said input control elements, said inertia means being connected to operate the other of said input control elements, and said output control element being connected to operate said pitch control system.

8. In a helicopter aircraft or the like, the combination comprising a plurality of bladed lift rotors mounted upon the aircraft, cyclic and collective pitch change mechanisms for each of said rotors, a collective pitch control 'system operatively connected to said collective pitch a function of the algebraic sum of the respective input magnitudes, said pilot-operable control means being connected to operate one of said input control elements,

said inertia means being connected to operated the other of said input control elements, and said output control element being connected simultaneously operate both of said pitch control systems.

9. The combination set forth in claim 8, wherein said cyclic pitch control system provides like adjustmentsv of said cyclic pitch change mechanisms, and said collective pitch control system provides oppositely directed adjustments of said collective pitch change mechanisms.r

10. In a helicopter aircraft or the like, the combination comprising a bladed lift rotor mounted upon the aircraft, cyclic and collective pitch change mechanisms for said rotor, a pitch control system operatively connected to said pitch change mechanisms for adjustments thereof, pilot-operable control means, inertia means mounted on said aircraft for movement relative thereto in response to acceleration of said aircraft in either vertical direction, and means including a differential mechanism operatively connecting both said pilot-operable control means and sai-l inertia means to said pitch control system for actuation thereof, said dilferential mechanism having a pair of independently operable input control elements and an output control element in which the output magnitude is a function of the algebraic sum of the respective input magnitudes, said pilot-operable control means being connected to operate one of said input control elements, said inertia means being connected to operate the other of said input control elements, and said output control element being connected to operate said pitch control system.

References Cited in the tile of this patent UNITED STATES PATENTS 2,092,424 Potez Sept. 7, 1937 2,432,348 Stalker Dec. 9, 1947 2,555,577 Daland June 5, 1951 2,629,452 Alex Feb. 24, 1953 FOREIGN PATENTS 706,796 France Man 31, 1931 838,413 France Dec. 7, 1938 880,122 France Dec. 18, 1942 

